1. Field of the Invention
The present invention relates to a data reception apparatus, a data transmission apparatus, and a method thereof, for receiving a transmission signal obtained by inserting a predetermined reference data at a predetermined cycle, performing orthogonal frequency division multiplexing (OFDM), and transmitting the result via a predetermined transmission line, compensating for the transmission characteristic of the transmission line by using the reference data, and demodulating the result.
2. Description of the Related Art
When transmitting digital data, generally a phase shift modulation method (PSK) wherein the phase of one carrier signal is brought into correspondence with the value of the transmission data to be transmitted or a quadrature amplitude modulation method (QAM) bringing the phase and amplitude into correspondence with the value of the transmission data, has been used. These methods are sometimes referred to as a single carrier method since a single carrier signal is used.
In addition to this single carrier method, a multi-carrier method such as an orthogonal frequency division multiplexing (OFDM) method performing the transmission of the digital data using carrier signals of a plurality of frequencies is now being used.
FIG. 1 is a view showing the configuration of a data reception apparatus 8 for demodulating transmission data SOUT from a reception signal SIN of the OFDM method.
As shown in FIG. 1, the data reception apparatus 8 is constituted by a demodulator 80 including a fast Fourier-Transformation circuit (FFT), a differential decoder 82, and a decoder 84. The data reception apparatus 8 demodulates an input transmission signal SIN (transmission signal of the OFDM method) transmitted via a transmission line (not shown) such as a cable communication channel, wireless communication channel, or broadcast channel, obtained by processing the transmission data and outputs the resulted as a decoded signal SOUT.
The transmission signal of the OFDM method is received from the transmission line by a reception circuit (not illustrated) positioned in front of the demodulator 80, is converted to a digital format, and applied as a received signal SIN to the demodulator 80.
The demodulator 80 applies fast Fourier transformation (FFT) to the received signal SIN to demodulate it and outputs the result as a demodulated signal S80 to the differential decoder 82. Note that, in the OFDM method, the transmission data is subjected to, for example, trellis coding modulation and further subjected to orthogonal frequency division multiplexing by inverse fast fourier transformation (IFFT) to make the transmission signal. Accordingly, by performing FFT on the transmission signal (received signal SIN), the transmission data before the orthogonal frequency division multiplexing can be demodulated.
The differential decoder 82 performs the differential decoding on the demodulated signal input from the demodulator apparatus 80 and outputs the result as the decoded signal S82 to the decoder 84.
The decoder 84 generates the branch metric of the differential decoder 82 and performs maximum likelihood decoding of the original transmission data based on this branch metric.
However, the demodulator 80, the differential decoder 82, and the decoder 84 of the data reception apparatus 8 shown in FIG. 1 perform individually independent processing, so the transmission characteristic of the transmission line with respect to the received signal SIN is not considered in the decoder 84. The decoder 84 compares the signal point on the signal plane of the decoded signal S82 and the assumed signal points to perform the maximum likelihood decision, so where the effect of the transmission characteristic is not considered, its capabilities cannot be completely exploited.